The field of orthodontics is concerned with repositioning and aligning a patient's teeth for improved occlusion and aesthetic appearance. For example, orthodontic treatment often involves the use of tiny slotted appliances known as brackets that are fixed to the patient's anterior, cuspid, and bicuspid teeth. An archwire is received in the slot of each bracket and serves as a track to guide movement of the teeth to desired orientations. The ends of the archwire are usually received in specialized appliances known as buccal tubes that are secured to the patient's molar teeth.
A number of orthodontic appliances in commercial use today are constructed on the principle of the “straight wire concept” developed by Dr. Lawrence F. Andrews, D.D.S. In accordance with this concept, the shapes of the appliances, including the orientation of the slots of the appliances, are selected so that the slots are aligned in a flat-reference plane at the conclusion of treatment. Additionally, a resilient archwire is selected with an overall curved shape that normally lies in a flat reference plane.
When the archwire is placed in the slots of the brackets in a straight wire appliance system at the beginning of orthodontic treatment, the archwire is often deflected upwardly or downwardly and twisted positively or negatively from one appliance to the next in accordance with the patient's malocclusions. However, the resiliency of the archwire tends to return the archwire to its normally curved shape that lies in a flat reference plane. As the archwire shifts toward the flat reference plane, the attached teeth are moved in a corresponding fashion toward an aligned, aesthetically pleasing array.
As can be appreciated, it is important for the practitioner using straight wire appliances to fix each bracket in the exact proper position on the corresponding tooth. If, for example, a bracket is placed too far in an occlusal direction on the tooth surface, the archwire will tend to position the crown of the tooth too close to the gingiva (gums) at the end of the treatment. As another example, if the bracket is placed to one side of the center of the tooth in either the mesial or distal direction, the resultant tooth orientation will likely be an orientation that is excessively rotated about its long axis.
The process of positioning and bonding the brackets to the patient's teeth requires considerable care, and requires the practitioner to visually determine the proper location of the brackets on the respective teeth. Often, in a technique known as indirect bonding, a practitioner determines bracket positions by the use of a ruler, protractor and pencil to measure and mark features on a plaster cast made from impressions of the patient's teeth. This process is often difficult to carry out with precision, and may be subjective in nature. Consequently, it is often difficult for the practitioner to ensure that the brackets are precisely positioned on the teeth at correct locations.